Variable self-inductance with a core of magnetic material



g- 4, 1942? H. WITTHOFT ETAL 2,291,780

VARIABLE SELF'INDUCTANCE WITH A CORE OF MAGNETIC MATERIAL Filed Aug. 28, 1940 INVENTORS f/AMS WITH/OFT, BERN/MRO DRiCl/Slil? (Fl/R7 l/ElA/IC/(E Hm-M/ ATTORNEY Patented Aug. 4, 1942 VARIABLE SELF-INDUCIANCE WITH A CORE OF MAGNETIC MATERIAL Hans Witthiift, Bernhard Drechsler, and Curt Heinicke, Berlin, Germany, assignors to Telefunken Gesellschaft fiir Drahtlose Telegraphie m. b. H., Berlin, Germany, corporation of I Germany Application August 28, 1940, Serial No. 354,580 In Germany July 1, 1939 1 Claim. (01.171-242 Some of the known types of variable inductances with a movable magnetic core have a small inductance range. Therefore also the frequency range is small. It is well known to overcome this disadvantage by using two coils connected in series and varying the self-inductance and additionally the mutual inductance by moving the iron core. In such known devices the two coils are so-far apart from each other that they are substantially not coupled together. The axis of the two coils lie parallel and the iron core is u-shaped and is movable into the two coils at v the same time.

Another known type of variable inductance comprises two coils connected in series and a magnetic core having the shape of a bar. The coils lie in the common axis to theright and to the left of the core. The variable inductance then has a minimum of inductance. The maximum of inductance is achieved by moving the core intoone of the coils and moving the other coil which has a coil.

The present invention is directed to a variable inductance arrangement which allows a variation of the inductance by rotation of ahandle using an endless cord.

The invention. will be better understood from the following description considered with the accompanying drawing.

Referring to the drawing Fig. 1 illustrates in schematic form the construction of the variable inductance; and,

Fig. 2 illustrates in schematic form a wiring diagram of an antennatuning arrangement using the variable inductance of Fig. 1.

In Fig. 1 the ironcore E is fastened to' the cylinder Z3 and pierced to take up the cord S. This cord S at the point a is fixed to acylinder of insulating material Zi carrying the coil SP1. At the point b the cord is fixed to'the cylinder of greater diameter over the first insulating material Z: carrying the coil Spa. The

inductance relative to the angle of rotation. For

padding the tuning, for instance with a tuning able relative to the wheel R1.

capacity of a following receiving circuit, the two ends of the cord are fastened to a disc Sch mov- In this manner the value of the lowest inductance is regulated.

Fig. 2 shows a wiring diagram employing the variable inductance according to the invention. The variable inductance L1 is connected into the antenna circuit and makes possible a tuning of the antenna circuit to the received frequency at the same time with the tuning of the input circuit L2, C2 by the tuning capacity C2. The antenna circuit is coupled to the input circuit with the capacity C as loosely as in a bandpassfilter.

Itis also possible to use an inductive coupling, however the capacitive coupling is better in an automobile-receiver because the bandpassfilter acts at the same time as a lowpassfilter with two filter sections for the short wave ignition disturbances. This wiring showing a bandpassfilter for the received frequency has the advantage that with the same antenna the voltage at the grid of the first tube is greater.

We claim as our invention:

In a variable inductance device, a pair of coaxially mounted, axially. displaceable coils connected in series in the same sense, the internal diameter of one of said coils being larger than the outer diameter of the other coil whereby the smaller thereof may be substantially completely inserted within the larger coil, a core of magnetic material for said coils, said core being mounted in co-axial relation with said coils, the diameter of said core being smaller than the internal diameter of the smaller coil, each of said coils being axially displaceable in relation to said core in oppositedirections between a position whereinthe core is substantially completely inserted said core being axially pierced thereby to permit both sections of the belt to pass therethrough,

one section of the belt being secured to one coil,

the other section of the belt being secured to'the second coil whereby said belt acts inone sense to displace said coils axially toward each other and in the other sense to displace said coils axially away from each other.

HANS wrrrnor'r.

BERNHARD DRECHSLER. CURT 

